Coherence, Transition, “Flow” Repeating, or “echoing” key words from preceding sentences is one of the most powerful tools you have for achieving “flow.” The basic technique is to “echo” a key word in the previous sentence toward the beginning of the new sentence. Actually, there are two kinds of sequencing methods (“flow” methods): Continuous focus Shifting focus Continuous focus Used to call this “static” focus, but “static” is pejorative: Mars is the fourth planet from the Sun in our solar system and is named after Mars, the Roman god of war. Mars is also known as the "Red Planet" due to its reddish appearance when seen from Earth. The prefix areo-, from the Greek god of war, Ares, refers to Mars in the same way geo- refers to Earth. Mars has two moons, Phobos and Deimos, which are small and oddly-shaped. Barely stifled yawns greeted the electronics novelty that was introduced to the public in mid1948. "A device called a transistor, which has several applications in radio where a vacuum tube ordinarily is employed, was demonstrated for the first time yesterday at Bell Telephone Laboratories," noted an obviously unimpressed New York Times reporter on page 46 of the day's issue. To be sure, the gadget had plusses. Not only could the transistor amplify electric current like a vacuum tube, it also used little power, didn't need to warm up, and was compact—a thimble-sized cylinder with a couple of protruding wires. But because its main ingredient was an expensive, hardto-handle element called germanium, the transistor seemed likely to remain a laboratory curiosity. Shifting focus Used to call this “dynamic,” but “dynamic” makes it sound superior, which it’s not. A solar cell (or a "photovoltaic" cell) is a semiconductor device that converts photons from the sun (solar light) into electricity. To achieve this conversion, the device needs to fulfill only two functions. One function involves photogeneration of charge carriers (electrons and holes) in a lightabsorbing material. The other function involves separation of the charge carriers to a conductive contact that will transmit the electricity. The result of the functions is called the photovoltaic effect, and the field of research related to solar cells is known as photovoltaics. The most important part of a solar heating system is the solar collector whose main function is to heat water to be used in space heating. There are various types of collectors. However, the flatplate collector is the most common and the focus of the following discussion. A flat-plate collector consists of a box-shaped black plate absorber covered by one or more transparent layers of glass or plastic with the sides and the bottom of the box insulated. These layer of glass or plastic have an intervening air space that produces the heattrapping effect. Water is heated as it circulates through or below the absorber component, which is heated by solar radiation. Topic strings These sequences of topics are known as topic strings: some are continuous; others are shifting. Which to use depends on what you are writing about. Mars Mars Mars Mars novelty transistor gadget transistor transistor solar collector types flat-plate collector layers heat Transition words In some cases, you cannot echo a preceding topic in a natural way. When that occurs, my theory is that we use transition words such as (but not limited to!) “however,” “therefore,” “for example,” or “in other words.” Analyzing topic strings When you have this way of analyzing coherence, you can see why some discussions—perfectly grammatical ones—are more difficult to follow than necessary: 1 The development of the transistor goes back to the nineteenth century. 2 Germanium and silicon, along with a number of other crystalline materials, are semiconductors, so-called because they neither conduct electricity well, like most metals, nor block it effectively, as do insulators such as glass or rubber. 3 Back in 1874 a German scientist named Ferdinand Braun identified a surprising trait of these on-the-fence substances: Current tends to flow through a semiconductor crystal in only one direction. 4 This phenomenon, called rectification, soon proved valuable in wireless telegraphy, the first form of radio communication. 5 When electromagnetic radio waves traveling through the atmosphere strike an aerial, they generate an alternating (two-way) electric current. 6 However, earphones or a speaker must be powered by direct (one-way) current. 7 Methods for making the conversion, or rectification, in wireless receivers existed in the closing years of the 19th century, but they were crude. 8 In 1899 Braun patented a superior detector consisting of a semiconductor crystal touched by a single metal wire, affectionately called a "cat's whisker." 9 His device was popular with radio hobbyists for decades, but it was erratic and required much trial-and-error adjustment.